Unusual records of marine organisms in the ... - acta.izor.hr

Unusual records of marine organisms in the Neretva River (Croatia and Bosnia and Herzegovina)

Pero TUTMAN1, Branko DRAGIČEVIĆ1*, Jakov DULČIĆ1, Luka GLAMUZINA3, Višnja BUKVIĆ2 and Josip VEKIĆ4

1 Institute of Oceanography and Fisheries, Laboratory for Ichthyology and Coastal Fisheries, Šetalište Ivana Meštrovića 63, 21000 Split, Croatia

2 University of Herzegovina, Blajburških žrtava 100, 88000 Mostar, Bosnia and Hercegovina

3 University of Dubrovnik, Department of Applied Ecology, Ćira Carića 4, 20000 Dubrovnik, Croatia

4 Nature Park „Hutovo blato“, Čapljina, Bosnia and Herzegovina

*Corresponding author, e-mail: [email protected]

This paper presents a review of the unusual occurrences of various marine species found upstream in the Neretva River and its wider delta zone in the last two decades. The occurrences of at least eight different marine species were reported by local fishermen, representing very rare records of these species in the upstream areas of rivers. Although some of these species generally inhabit both saltwater and brackish waters, their occurrences high upstream are probably the consequence of changes in hydrological conditions in Neretva River. Namely, more intense saltwater intrusion into the river observed in the last two decades provides suitable conditions for mass penetration of euryhaline organisms high into the Neretva River. In this biodiversity rich area which hosts a sig-nificant number of endemic species, such phenomena can threaten the local freshwater communities.

Key words: saltwater intrusion; indicator species; east Adriatic watershed

ISSN: 0001-5113AADRAY

ACTA ADRIAT.,62 (2): 139 - 148, 2021 ORIGINAL SCIENTIFIC PAPER

INTRODUCTION

Species that normally inhabit river mouth areas are usually adapted to withstand varying salinity conditions and can occasionally be found deep upstream inland, but in relatively small numbers when compared to their abundance in more saline waters. However, the unusual pres-ence of marine species in untypical habitats like rivers deep inland, usually indicates significant

habitat alterations that are often conditioned by anthropogenic or natural processes (ROMAÑACH et al., 2019). This is especially indicative when marine species which are not adapted to tolerate highly fluctuating environmental salinity levels due to their physiological tolerances are found in upstream portions of rivers.

Saltwater intrusion represents the flow of seawater into coastal river flows as a result of natural processes or human activities and is

140 ACTA ADRIATICA, 62 (2): 139 - 148, 2021

one of the most significant global challenges for coastal water resource managers, industries, and agriculture (MONTANARI, 2015). The impact of the saltwater intrusion on local biodiver-sity in brackish and freshwater ecosystems is a subject of increasing international concern because of its adverse environmental impacts (see in NICHOLLS & CAZENAVE, 2010). This con-cern arises mainly because saltwater intrusion has negative impacts on coastal environments, including loss of habitat for freshwater biota such as vegetation, phyto- and zooplankton and fishes, as well as the associated penetration of brackish and saltwater organisms (LOVE et al., 2008). Despite the evident influence caused by changes in salinity in many coastal areas (CAL-VACHE & PULIDO-BOSCH, 2017) and their impacts on local biodiversity (LOVE et al., 2008, PIZANO-TORRES et al., 2017), studies relating to individual records of marine species in areas of reduced salinity are mostly lacking (ABDUL-RAZAK & INTISAR, 2019). Nevertheless, observations of strictly marine species in upstream portions of rivers could indicate alterations in riverine hydrological conditions and provide insight into geographical extent of such phenomena.

The Neretva River and its delta are one of the most important biodiversity and agricultural areas in the Mediterranean karst area of Croatia (MRAKOVČIĆ et al., 2006) and Bosnia and Her-zegovina (GLAMUZINA et al., 2013). Relatively shallow area of its wide delta supports a rich faunal diversity and hosts important spawn-ing and nursery grounds for many fish species which makes it also a very important fishing area (GLAMUZINA, 2010, DULČIĆ & GLAMUZINA, 2010; MATIĆ-SKOKO et al., 2010). This area also hosts several protected ornithological and ich-thyological reserves and is considered one of the most important wetlands in Europe as a resting and wintering place for migratory birds (SMITH & DARWAL, 2006; STUMBERGER & SCHNEIDER-JACOBY, 2010). In 1991, the Neretva River Delta was listed as a Wetland of International Impor-tance under the Ramsar Convention. This area is also one of the eight Specially Protected Areas under the Barcelona Convention, as well as an important area for birds in Europe which hosts at

least 115 nesting species (TUTIŠ et al., 2013). How-ever, in the last decades, due to modifications in salinity regimes of the surface and ground waters, the lower Neretva River has under-gone numerous environmental changes (ROMIĆ et al., 2008, 2018, 2019). This area was addition-ally impacted by recurrent droughts, increased levels of urban pollution (GLAMUZINA, 2010) and the effects of the uncontrolled introduction of freshwater and marine non-native species (GLA-MUZINA et al., 2020). It was found that seawater penetrates along the Neretva riverbed in a sepa-rate bottom layer of saltwater upstream up to about 25 km from the river mouth (LJUBENKOV & VRANJEŠ, 2012, ROMIĆ et al., 2018, 2019). The water quality of the lower course of Neretva is influenced by the complex water regime in the lower course of Neretva River which is a con-sequence of various factors such as hydroelec-tric system on the upstream side, reduction of groundwater inflow from river Trebišnjica and deepening of the Neretva riverbed. Also, sea-level rise due to global warming is an additional factor causing increased salinity in the Neretva basin (IVANKOVIĆ et al., 2017).

The presence of certain euryhaline marine species which can tolerate lower salinity is usual in river deltas and transitional waters, however, the presence of stenohaline, or strictly marine species, in lower river course can indicate sig-nificant hydrological alterations. Such species generally very rarely enter waters of reduced salinity due to their physiological limitations. In this paper, we present the review of the unu-sual occurrences of some typical marine species found far upstream in the Neretva River in Croa-tia and Bosnia and Herzegovina. Due to lack of monitoring programmes in the area which could provide data collected in situ and in such a way shed more light on the extent of penetration of marine species in the area, data on these occur-rences were collected mostly through direct contacts with local citizens and by searching social networking sites and internet news portals for reports on unusual occurrences. Such way of data collection has already proven to be valuable in the early detection of alien species in the area (DULČIĆ et al., 2018, TUTMAN et al., 2021).

141TUTMAN et al: Unusual records of marine organisms in the Neretva River (Croatia and Bosnia and ...

Here we will provide a brief outline of species whose presence has been reported and discussed in the paper. Common jellyfish Aurelia aurita (Linnaeus, 1758) is a cosmopolitan organism of oceanic and coastal waters as well as warm tropical waters ranging from North and South America, Eurasia, southern Greenland, and likely all coasts of Australia (BREKHMAN et al., 2015). European squid Loligo vulgaris Lamarck, 1798 occurs abundantly in coastal waters from the North Sea to at least the west coast of Africa from sea level to depths of 500 m including the Mediterranean Sea (JEREB et al., 2010). European cuttlefish Sepia officinalis Linnaeus, 1758 is generally found from the eastern North Atlantic south into the Mediterranean Sea, along the west coast of Africa as far to South Africa, dwelling in sandy or muddy substrates from subtidal waters to depths of 200 meters (JEREB & ROPER, 2005). The common octopus Octopus vulgaris Cuvier, 1797 is a mollusk species with worldwide distri-bution; abundant in coastal waters and the upper part of the continental shelf of tropical, subtropi-cal, and temperate waters between the surface and a depth of 100 to 150 meters in the Mediter-ranean Sea, the Eastern Atlantic Ocean, and in Japanese waters (MANGOLD, 1983). The brown ray Raja miraletus, Linnaeus 1758 is distributed subtropically in the eastern Atlantic Ocean from northern Portugal and throughout the Mediter-ranean, south to Madeira and South Africa. It is quite common on the continental shelf from Por-tugal throughout the Mediterranean and along the western and southeastern coasts of Africa. This benthic fish is found in brackish and marine waters up to depths of 300 m, most commonly from 50-150 m. The brown ray resides over soft bottom habitats along the coastal shelf and the uppermost slope. It is a common species in the wider area of the Neretvanski channel into which the Neretva River flows (MATIĆ-SKOKO et al., 2010). The common pandora Pagellus eryth-rinus (Linnaeus, 1758) is fish species found up to 200-300 m of depth on various bottoms from Eastern Atlantic and the Mediterranean to Guinea-Bissau (BAUCHOT & HUREAU, 1990). The annular sea-bream Diplodus annularis (Lin-naeus, 1758) is a gregarious fish species wide-

spread in the Mediterranean Sea and the Eastern Atlantic Ocean; it inhabits rocky, sandy bottoms and seagrass beds (BAUCHOT & HUREAU, 1990). Family Soleidae consists of widely distributed flatfish species of which some also occur in the Adriatic Sea. The majority of Soleidae species inhabit saltwater soft bottoms but can also be found in brackish waters (DULČIĆ & KOVAČIĆ, 2020). There is currently no information on the entry of these species high inland into upstream portions of rivers.

MATERIAL AND METHODS

Occasional records of marine species found upstream in the Neretva River in the last two decades were obtained opportunistically directly by the authors (V. BUKVIĆ, P. TUTMAN & L. GLA-MUZINA.) who were contacted by local citizens after collecting or catching the species. In such a way records of Solea sp., Aurelia aurita, Pagellus erythrinus, Sepia officinalis, Diplodus vulgaris and Loligo vulgaris were collected. Reports of unusual catches made by the local fishermen were usually accompanied with addi-tional data such as the temporal and spatial extent of observations of marine species in Ner-etva river.

An online search was also performed in order to extract additional records which appeared on the internet. In such a way, records of Raja miraletus and Octopus vulgaris were detected as they appeared in online news articles.

All species described herein were identified from provided photos of specimens. Unfortu-nately, neither of the listed species have been preserved for analysis and data such as water salinity and temperature were not collected.

RESULTS AND DISCUSSION

In total, occurrences of eight marine species have been recorded in the upstream areas of Neretva River. In Table 1 details on the occur-rences as well as the indication of the source of information are provided. In Fig. 1 geographical locations of records are presented. Majority of records were communicated directly to the sci-

142 ACTA ADRIATICA, 62 (2): 139 - 148, 2021

entists by the local citizens, mainly recreational fishermen, who are regularly fishing in the area.

More frequent appearances of marine species in the area of Neretva river began about 15 years ago with the occasional occurrences of Solea sp. in the town of Metković, 20 km upstream and the unusual finding of Octopus vulgaris near the Kula Norinska settlement about 15 km upstream from the river mouth. Afterwards, occasional findings of Loligo vulgaris and Sepia officinalis were reported from the area. It should be noted that these species are known to inhabit brackish waters, however, no scientific publication has previously reported their occurrence from any European upstream freshwater ecosystem.

In November 2019, an interesting catch of a specimen of ray species has been reported on a website of local radio Čapljina (Bosnia and Herzegovina). The specimen was caught in the Neretva River near the small settlement Višići (Bosnia and Herzegovina), about 25 km upstream off Neretva River mouth (43°03’38.50 N, 17°42’00.19 E; Fig. 2). The specimen was found alive in the shallow water on the muddy bottom and was caught by hand. It was identi-

Fig. 1. Locations of records: (1) Aurelia aurita, (2) Loligo vulgaris, (3) Sepia officinalis, (4) Octopus vulgaris, (5) Raja miraletus, (6) Pagellus erythrinus, (7) Diplodus vulgaris, (8) Solea sp.

Fig. 2. Specimen of Brown ray Raja miraletus caught on 7th November 2019 in Neretva River near town of Čapljina, approximately 25 km inland in Bosnia and Herzegovina. White arrow indicates the specimen (Photo: Radio Čapljina).


fied from the photo as Brown ray, Raja mirale-tus on the basis of visible morphological char-acters described by STEHMANN & BÜRKEL (1984). It measured approx. 40 cm in total length and weighed approx. 400 g. The record of R. mirale-tus so high upstream inland in the Neretva River represents also a curiosity in the context of the distribution of this species. Although according to FROESE & PAULY (2021) this species can be found in brackish waters, there is no evidence of it being recorded in rivers high upstream.

Fig. 3. Specimen of European squid Loligo vulgaris caught on 19th April 2020 in Neretva River near town of Metković, approximately 20 km inland in Croatia. (Photo: Višnja Bukvić)

Table 1. Details on the marine species records observed in the upstream portions of Neretva River

No. Classification Scientific name

Locations of catch

Date of record Remarks Source

Fishermen perceptions of trends

1. Cnidaria/Scyphozoa

Aurelia aurita(Linnaeus, 1758)

Kula Norinska (Croatia)

21.7.2012 4 specimens caught

Fisherman report

From 2012, now relatively common

2. Mollusca/Cephalopoda

Loligo vulgaris Lamarck, 1798

Metković (Croatia) 19.4.2020 1 specimen

caughtFisherman report

First observed in 2010, now very common, regular occurrence


Sepia officinalisLinnaeus 1758

Opuzen, Kula Norinska, Metković (Croatia)

21.7.2019 n/a Fisherman report

Present from 2017, appears periodically and is caught in moderate quantities in the area


Octopus vulgaris Cuvier, 1797

Opuzen (Croatia) July, 2014 1 specimen Internet

portal

Periodical appearance since 2014, several records

5. Elasmobranchii/Rajiformes

Raja miraletus Linnaeus, 1758

Višići (B&H) 8.11.2019 1 specimen Internet

portalSingle record in 2019

6. Actinopterygii/Perciformes

Pagellus erythrinus, Linnaeus, 1758.

Kula Norinska, Metković (Croatia)

15.4.2020 Caught in set gill nets

Fisherman report

From 2016 relatively common; appears regularly in the nets in small but persistent numbers

7. Actinopterygii/ Perciformes

Diplodus annularis, Linnaeus 1758.


17.5.2020. n/a Fisherman report

From 2017; not in substantial numbers, but regular appearance

8. Actinopterygii/ Pleurinectiformes

Solea sp. (Linnaeus, 1758)


7.6.2020. n/a Fisherman report

From 2008 appears regularly, increasing in numbers

144 ACTA ADRIATICA, 62 (2): 139 - 148, 2021

In the vicinity of the Metković bridge, on 19th April 2020, a fisherman caught a large specimen of Loligo vulgaris (Fig. 3), which measuired 36 cm in length and weighed 650 g. According to fisherman, this species is also occasionally caught near Kula Norinska in larger numbers and smaller sizes. This specimen was caught about 20 km upstream from the Neretva river mouth.

The unusual occurrences of marine species so high upstream are the possible indicators of changing riverine freshwater conditions. More frequent records of marine species in this area are most likely related to the ongoing process of more intense decline in freshwater flow and high saltwater intrusion observed in the last two decades (ROMIĆ et al., 2008, 2018, 2019). Saltwater intrusion is often followed by the penetration of typically marine species into freshwater zones of the delta. If salinity increases more frequently in the Neretva River, mass penetration of euryha-line organisms high into the Neretva River may soon be expected threatening the local fresh-water fish community, among which there is a significant number of endemics (GLAMUZINA et al., 2013). The salinity in the delta section of the lower Neretva River has increased since the construction of a large hydroelectric project in upper Neretva River (so called Upper Horizons). As a result of the partial slowing of the river flow, the discharge of the Neretva River at its mouth is reduced by an average of 25% annu-ally (ROMIĆ et al., 2008, 2018, 2019) which causes a shift of the upstream limit of the saltwater intru-sion in the Neretva River. Hence, lower Neretva River has suffered from significant regression in freshwater water influx related to the decline in rates of discharge from upper areas during the past years. The saltwater intrusion upstream extends at least to settlement Gabela in Bosnia and Herzegovina where a specimen of sea lam-prey Petromyzon marinus has beend recorded in 2013 (GLAMUZINA et al., 2019). During the period of increased salinity, an increase in the num-ber of euryhaline species such as Pomatomus saltatrix, Platichthys flesus, Sparus aurata and Dicentrarchus labrax was recorded in the lower reaches of the Neretva (GLAMUZINA et al., 2020).

However, the new reports and persistence of freshwater-dependent species in Neretva River delta (DULČIĆ et al., 2017, TUTMAN et al., 2021) sug-gests that there may be a time lag in the response of freshwater-dependent species to increasing salinities. Salinization is a widespread phenom-enon in the environment, which threatens many taxa (CALVACHE & PULIDO-BOSCH, 2017, ABDUL-RAZAK & INTISAR, 2019).

Various online media and social networks can act as a potential source of information for documenting biodiversity, providing valu-able information sources which can allow early detection of unusual species, that would oth-erwise go unnoticed (BARVE 2014, DULČIĆ et al., 2017, 2018). For example, occurrences of non-native Micropterus salmoides (DULČIĆ et al., 2017) and Synodontis eupterus (DULČIĆ et al., 2018) recorded in Neretva, have been brought to the attention of scientists through reports on the social network. Also, scientists should reach to local people as their knowledge on the local eco-systems usually contains a wealth of information that can complement other sources and improve monitoring and action plans in the context of aquatic invasions.

Records of marine species in a usually strictly freshwater ecosystem are a valuable indication of environment alteration which can indicate the extent to which saltwater intrusion phenomena influences local biodiversity. The result of a recent study (GLAMUZINA & DOBROSLAVIĆ, 2020) points to the fact that major Neretva flow of 20 km in length from the river mouth is under sea-sonal summer impact of seawater, which leads to salinization and complete marinization of this ecosystem during the warm period of the year.

Restoring freshwater flow in cooperation with hydroelectric power management to com-bat saltwater intrusion may help to retain a salin-ity balance that is essential for the preservation of the freshwater fish communities of the lower Neretva River. Results from this study are fun-damental in enhancing the understanding and documentation of unusual biodiversity findings driven by saltwater intrusion effects, and can also serve as key information during the action and planning of the implementation of hydro-


logic restoration and management activities in the lower Neretva river and its delta. Addition-ally, as already stated by ARVELUND (2009) the shift in ecology and biogeography of marine fish species at the beginning of the 21st century may hypothetically be a useful indicator for climate change

ACKNOWLEDGEMENTS

This work has been fully supported by Croa-tian Science Foundation (HRZZ) under the pro-ject IP-2016-06-5251.

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Received: 26 August 2021Accepted: 28 October 2021

148 ACTA ADRIATICA, 62 (2): 139 - 148, 2021

Neobični nalazi morskih organizama u rijeci Neretvi (Hrvatska i Bosna i Hercegovina)

Pero TUTMAN, Branko DRAGIČEVIĆ*, Jakov DULČIĆ, Luka GLAMUZINA, Višnja BUKVIĆ i Josip VEKIĆ

*Kontakt e-pošta:[email protected]

SAŽETAK

U radu je prikazan pregled neobičnih nalaza morskih vrsta u rijeci Neretvi te širem području njene delte u posljednja dva desetljeća. Pojava najmanje 8 različitih morskih vrsta prijavljena je od strane lokalnih ribara, a radi se o općenito rijetkim nalazima morskih organizama u uzvodnim dije-lovima riječnih tokova. Iako neke od vrsta opisanih u radu obitavaju i u slanim i u bočatim vodama, njihova pojava visoko uzvodno vjerojatno je posljedica promjena hidroloških uvjeta u rijeci Neretvi.

Naime, intenzivniji prodor morske vode u rijeku u posljednja dva desetljeća omogućava masovno prodiranje eurihalnih organizama visoko u rijeku Neretvu. Na ovom području, bogatom biološkom raznolikošću sa značajnim brojem endemskih vrsta, takve pojave mogu ugroziti zajednice slatko-vodnih organizama.

Ključne riječi: intruzija slane vode; indikatorska vrsta; sliv istočnog Jadrana

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